Wireless telephone system

ABSTRACT

A wireless telephone communication system for wireless, voice, data or voice and data terminals comprising apparatus at a central location for receiving one or a plurality of signals for communication with selected ones of wireless communication terminals, apparatus for converting the signals to spread spectrum radio frequency signals, a leaky transmission line located in a communication region, apparatus for applying the spread spectrum radio frequency signals to the transmission line for electromagnetic radiation within the region, at least one wireless communication terminal adapted to receive a predetermined one of the spread spectrum radio frequency signals and for demodulating it into an intelligible signal.

This invention relates to a telephone communication system utilizingwireless voice, data, or voice and data terminals.

It is often difficult to provide telephone service to personnel who arecontinuously moving, yet must be quickly available at a telephone ordata terminal, e.g. warehouse stock takers, personnel responsible forbuilding maintenance or security, etc. Paging receivers have been usedto summon such personnel to call a number via the closest telephone set.Sometimes such personnel are required to enter data into a terminal forstorage at a central computer. Yet wired jacks for interfacing atelephone with a PABX or terminal to a computer are often spaced atsubstantial distances from each other in warehouses, for example.

Voice communication of such personnel has been partly solved by the useof cordless (wireless) telephones each operating at a differentfrequency from the other. However such telephones have exhibitedsubstantial problems. There are usually a limited number of channelsavailable, limiting the number of telephone/wireless receiver sets whichcan be used in a given area. Often interference from adjacent channelsor other services is encountered. Transmission or reception nulls areoften encountered when a cordless telephone is oriented in a particulardirection relative to the main transmitting and receiving station. Suchnulls are also caused by shielding by steel and concrete of which thebuilding housing the system is built. The system lacks privacy; sincethe common radio bands are used, the signals can be readily intercepted.

In addition, the use of wireless presents a range problem. Particularlyfor large areas, such as when an entire building, a large warehouse, oraircraft hangar, etc., is to be covered by the system, a high poweredcentral transmitter could be used. However the power of the transmittercannot be greater than a level prescribed by the regulatory agencies.This places a limitation on the communication range. In the event thatmany low power transmitters are used scattered around the building, thecost increases substantially.

In the system described in U.S. Pat. No. 4,462,113 issued July 24, 1984,domestic A.C. power lines are used as an antenna for a low powertransmitter. However in this case the null problem still exists, and inaddition there is a severe bandwidth limitation to below approximately150 or 200 kHz. Further, transmission of signals via the A.C. powerlines is notoriously insecure, since such signals are often carried bythe power lines to neighbouring offices and buildings.

Due to the inherent lack of security, nulls and power/distancelimitations, the use of a mobile telephone handset has been limited tothe home environment, or to very special applications Until the presentinvention was made it had not yet been found suitable for commercialapplications in which, for example, an entire multi-story buildinghousing many different companies, some possibly being competitors witheach other, could be served mobile telephone and data services reliablyfrom the same PABX. Such prior art systems could not ensure completesecurity of communications, sufficiently low power radiation outside theconfines of the building, and absences of nulls or fade areas withinstructures.

Clearly for the above reasons portable terminals could also not be usedfor reliable transmission and reception of data to a central computer.

The present invention provides a communication system which can beconnected to a PABX switching system, which solves the problems notedabove. In addition to the provision of secure mobile (wireless)communications in a low power environment with the substantialelimination of the null or fade areas, it provides multi-channelwideband communications which can reliably carry voice, data andsignalling (supervisory) signals.

According to the present invention leaky transmission cables are used toradiate and to receive communication signals within the communicationregion. While at single frequencies such cables exhibit nulls along thecables at regular intervals, the communication signals which are carriedand which are received in the present invention are spread spectrum.

The use of spread spectrum signals carried by a leaky cable transmissionsystem achieves several highly desirable results. Firstly, nulls arevirtually undetectable or are eliminated due to the spreading of thesignals over a wide bandwidth. Secondly, since pseudo-noise bandwidthspreading (correlation) code is used for each channel, privacy ofcommunications is virtually assured as well as immunity frominterference between channels.

Since a leaky cable is used to distribute the signal in thecommunication region, the transmitter power and resulting effectiveradiated power can be very low. Furthermore, the power which is used isspread amongst the frequencies of a wide bandwidth, further reducing thepower used at any one frequency. Thus the interference that may becaused to other radio signals outside of the building is virtually nil.Also the radiated power within the building can be increased to asubstantial degree in comparison with a non-spread spectrum, single ormulti-point antenna transmitter to minimize the bit error rate, yet theeffective interference with external or other wireless services remainsvirtually nil, while the reliability of communication within thebuilding is increased.

The spread spectrum-leaky cable system according to this invention canoperate side-by-side with other similar systems or with conventional AMor FM wireless systems with substantially no or minimal interference.The maximum interference which might be apparent in such other systemswould merely be an increase in the background noise level.

The various handsets or wireless remote terminals to be used in thepresent system are preferred to be accessed by address code on asupervisory channel, and to be controlled to internally select apseudo-noise correlation code which matches a predetermined channeltransmit pseudo-noise spreading code. This type of system would benefitby the use of universal wireless handsets or terminals. However inanother type of system each handset or terminal is channel fixed with apredetermined pseudo-noise correlation code circuit, and the head endterminal changes its transmit pseudo-noise spreading code to suit thatof the selected handset.

In the reverse transmission direction which uses a different RF centrefrequency the mobile handset is either fixed with a transmitpseudo-noise spreading code for encoding the transmitted signal, or itcan be caused to transmit on a channel selected by the head end undercontrol of the head end via signals on the supervisory channel.

Leaky cable transmission systems have long been used to communicate intunnels and mines. One such system is described in U.S. Pat. No.4,476,574 issued Oct. 9, 1984. A large number of publications is listedin that patent which will provide background information to the readeron the use of leaky feeder communication systems both subsurface andabove the surface of the earth. However those systems suffer from one ormore of the problems described above which restrict them from use in areliable commercial communication system. A text which describes leakyfeeder systems is LEAKY FEEDERS AND SUBSURFACE RADIO COMMUNICATIONS byP. Delogne, IEE Electromagnetic Waves Series 14, 1982 Peter PeregrinusLtd.

Spread spectrum systems have been used in wireless systems in the past,as well as in certain specialized wired systems. A wireless spreadspectrum system is described in U.S. Pat. No. 4,455,651 issued June 19,1984 and in U.S. Pat. No. 4,086,504 issued Apr. 25, 1978. However inboth those cases the power limitation problem and the null problemdescribed above did not present problems, since in the first casedirectional antennas were used, and in the second case high power couldbe used and the system was not used in a communication system of thepresent kind. Furthermore, the locations of the various transmittingstations used in the latter patent, which relates to a seismicexploration system, can all be tested for proper spectrum prior to useand the transmitters moved in case a null is encountered. In addition,the locations of the spread spectrum transceivers are all fixed andpreknown, since they are used for triangulation purposes.

Spread spectrum systems have also been used in wired systems. Forexample in U.S. Pat. No. 4,438,519 issued Mar. 20, 1984, a spreadspectrum system is used connected to an A.C. power line, which is not aleaky feeder transmission cable, but constitutes an antenna. In thatpatent, however, it is clear that the bandwidth of the power line isvery low, and the transmission region is limited to areas which are notisolated by a transformer. Hence such systems are not useful for wideband multi-channel voice and data communication systems.

A spread spectrum signal is applied to telephone lines in the inventiondescribed in U.S. Pat. No. 4,475,208 issued Oct. 2, 1984. In this systemdata signals are converted to spread spectrum and are transmittedsimultaneously with voice over already existing telephone lines whichare not leaky feeder transmission cables . The bandwidth of suchtelephone lines is so low that the data signals are of very low bitrate. Clearly the system is not suitable for use in multi-channel widebandwidth transmission. In addition, the system is unsuitable for usewith wireless handsets or terminals since the telephone transmissionlines cannot carry radio frequency signals for any significant distance.

A general description of the history and structure of spread spectrumsystems will be found in the publication SPREAD-SPECTRUM COMMUNICATIONS,edited by Charles E. Cook et al, published by the IEEE Press, Instituteof Electrical and Electronic Engineers, Inc.

Carriage of a plurality of spread spectrum communication signals, eachmodulated by a different pseudo-random spreading or correlation code, bya leaky cable transmission system thus provides a new form of wirelessmobile voice and data communication system previously not thoughtpossible, that is, a reliable, private and low power communicationsystem using a large number of noted telephone handsets that can becarried within a predefined environment which can be used sharing thesame bandwidth as other commercial wireless services withoutinterference between the two kinds of systems. Such a system for thefirst time is viable within a building structure, i.e. steel andconcrete, which previously would not reliably support reliable wirelesscommunication to the required degree.

Because of the broadband and multi-channel capability of the presentsystem, the various mobile telephone sets can be provided with a fullrange of features normally made available only to wired telephone setsby the PABX, such as local alphanumeric display, conferencing,abbreviated dialing, etc., as well as computer access, remote control ofvarious apparatus such as automatic door locks, etc. Such features arenot now possible with the well known cordless telephones. A 32 channelsystem of the type described herein could give typically 200 users at asite mobile telephone facility depending on traffic. Further, thecommunication channel between the remote mobile unit and a PABX whichconnects to a larger computer can provide to the remote unit enormouscomputational power which would otherwise not be available in a handheld computer due to its size and cost limitations, and since a largeshared data base can be stored at the central computer.

A preferred embodiment of the invention is a wireless communicationsystem comprising apparatus at a central location for receiving one or aplurality of signals for communication with selected ones of wirelesscommunication terminals, apparatus for converting the signals to spreadspectrum radio frequency signals, a leaky transmission line located in acommunication region, apparatus for applying the spread spectrum radiofrequency signals to the transmission line for electromagnetic radiationwithin the region, at least one wireless communication terminal adaptedto receive a predetermined one of the spread spectrum radio frequencysignals and for demodulating it into an intelligible signal.

The invention also facilitates any of the wireless communicationterminals to initiate a communication with the central location, such acommunication being capable of having as its final destination anytelephone connectable to the central location, including others of thewireless communication terminals.

A better understanding of the invention will be obtained by reference tothe detailed description below of the preferred embodiment, withreference to the following drawings:

FIG. 1 is a general block diagram of a system according to the presentinvention,

FIG. 1A illustrates a code arrangement used in multiplexing the channelsof the spectrum,

FIG. 2 is a block diagram illustrating the mobile handset according tothe preferred embodiment of the invention,

FIG. 3 is a block diagram if the central equipment according to thepreferred embodiment of the invention, and

FIG. 4 is a block diagram of a preferred form of transmit channel usedin the system.

To briefly review the spread spectrum concept, this technique causes thespectrum of the transmitted signal of each channel to be spread over agreater amount of bandwidth than would be the case if time or frequencydivision multiplexing techniques were used. Indeed, the signals of allof the channels used are spread over the same band. This is achieved bymultiplying a generated data stream to be transmitted by a sequence withthe correct auto-correlation and cross-correlation properties(pseudo-random/noise code sequence). The resulting output signal is thenasequence having a higher data rate than that of the input data stream,which when used to modulate some form of amplitude, frequency or phaseshift keyed system, causes the spectrum to be spread over a widebandwidth.

At the receiver the incoming signal is multiplied by the samepseudo-random/noise sequence and the spectrum becomes despread to itsoriginal bandwidth. It is important to note that any interfering signalisspread at the receiver rather than despread The signal is thenfiltered at the receiver to the original bandwidth, leaving the originalsignal intactbut the interfering signal is attenuated and thus itseffect is diminished.This occurs whether the interfering signal is areal signal or is a hole (i.e. null) in the spectrum generated by somepropagation effect. Thus a spread spectrum system provides not onlyimmunity against interfering signals but also protection against holesin the spectrum.

Because a large number of spread spectrum sequences are generally known,itis possible to choose a set for a system which would be very difficultto decode by an intruder or eavesdropper. The spread spectrum systemtherefore contains its own intrinsic security The interference to whichthe system is immune may of course be other channels of the system usingthe same spectrum. Spread spectrum is therefore intrinsically amultiplexing system. Different channels using the same bandwidth can beimmune to each other if they use different spreading sequences formodulation and demodulation.

For example, for a pseudo random code having length 255 bits, there areprobably approximately 40000 codes which are strongly orthogonal, andthusare highly secure. It is preferred in the present system to use acentre frequency of between about 150 mHz to 1000 mHz, although theinvention is not limited to this band, each channel being approximately32 kHz wide, inwhich the voice signals are digitized in a well knownmanner. The spread channel is preferred to be 8 mHz wide.

Turning now to FIG. 1, the basic system according to the invention isillustrated. Within the confines of a building periphery 1 a leaky cable2is laid. The leaky cable can be coaxial cable with holes in its shield,such as described in Canadian Pat. No. 1,014,245 issued July 19, 1977,or other types of leaky transmission cables as described in theaforenoted text by P. Delogne. The cable can be sinuously laid above thefalse ceiling over the entire width and breadth of the building, canextend downthe centre of a narrow building, and can pass from storey tostorey in a multi-storey building as well as extend over the ceilingarea of a building. The leaky cable can be located within movable wallsor within anelectromagnetically transparent floor. Clearly the locationof the cable isdependent on the region to be covered and many variationsare possible. Theimportant aspect of the placement of the cable is thatfor a given minimum electromagnetic field strength, the entire workingarea of the building which defines the communication region should beenveloped by the field strength leaked from the cable which is above theminimum level.

It will be seen that since the field strength drops off by between thesquare and the cube of the distance from the cable, the effectiveradiatedpower outside the building periphery will be low or virtuallynil.

As central equipment, feeding the cable at one end is a transmitter 3,and receiving signals from the other end of the cable is a receiver 4.The input to the transmitter 3 is connected to a PABX 5 and the outputof receiver 4 is connected to the PABX 5. Also connected to the PABX aretrunks 6 and local telephone sets 7. Of course the PABX can be dividedby number code so that groups of local telephone sets 7 can beassociated with one business or division while other groups can beassociated with another business or division, if desired.

One or a plurality of remote wireless mobile telephone sets 8 arelocated within the building. These telephone sets will be referred toherein henceforth as mobile sets and can include data originating andreceiving terminals as well as, or in place of voice handsets. Mobilesets 8 preferably are battery operated, can be carried by a user, can belocated on a desk, hung on a wall, etc. They are not connected by wireto the telephone system PABX.

Depending on the characteristics of the leaky cable 2, its length, etc.,repeaters 9 may be required to be connected at regular intervals inserieswith the leaky cable. These repeaters are preferably wideband,such as CATVtelevision repeaters.

The PABX 5 is primarily a normal PABX which operates to interconnectlocal telephone sets with each other or with trunks 6. In order tocommunicate with the mobile sets 8, one of the telephone sets 7 dials anappropriate extension number designating a mobile set. The PABX, insteadof connectingthe telephone set to one of the other sets 7, simplychooses a line terminal 10 which corresponds to the mobile sets 8,connected to a predetermined junctor. The selected line terminalconnects to the input oftransmitter 3. In one embodiment ringing currentis applied to the line terminal in the normal manner. The transmitter 3converts the ringing current to a predetermined digital code,interleaves it with other digitalcodes on a supervisory channel,converts the resulting signal to a spread spectrum supervisory channelsignal and applies the resulting signal to the leaky cable 2.

The line terminal however designates which mobile set is to be selected,since it corresponds to the dialed number. Once the line terminal hasbeenselected the transmitter prefixes the digital code with anidentifier code which is unique to the mobile set. However it should benoted that rather than using line terminals, junctors of the PABX can beused. Also, insteadof applying ringing current to the terminal it canapply a ringing enable signal to a ringing terminal associated with theline terminal.

The signal radiates from the leaky cable into the communication regionwithin the building periphery 1, and is received by all of the sets 8.Allof the mobile sets continuously decode the signalling signals, and assoon as the identifier prefix which identifies the designated set hasbeen received, that the identified set converts the remaining code whichcalls for it to ring. Ringing is effected in the mobile set by keying aninternal "warble" or other signal to alert the user in a well knownmanner.

The user upon hearing the ringing signal, switches his mobile set on,the equivalent of going off hook. That mobile set then generates anoff-hook supervisory code which is converted to a spread spectrum R.F.signal in the signalling channel, and is transmitted via its own smalllocal antennato the leaky cable 2. Preferably the signal is sent withina time slot designated by the synchronization and control signals senton the aforenoted supervisory channel. Polling and response of themobile sets insequence is preferred to be used in the supervisorychannel.

The spread spectrum off-hook code is received by the leaky cable, and iscarried to the input of receiver 4. Receiver 4 demodulates, despreadsand decodes this signal and applies the off-hook supervisory signal tothe line input port 11 of PABX 5 associated with terminal 11 (or to theassociated junctor).

It should be noted that while two unidirectional ports 10 and 11 havebeen indicated, the transmitter and receiver can equally be connected toseparate inputs of a hybrid which is connected to a bidirectional lineor junctor.

The PABX 5, receiving the off hook supervisory signal as if it were froma telephone set, completes the connection between the calling party andmobile set via the transmitter 3 and receiver 4 as if it were to beconnected to another telephone 7. The transmitter 3 and receiver 4 areassociated with fixed voice channel transmit and receive pseudo-randomspreading codes. When this occurs control apparatus associated withtransmitter 3 and receiver 4 transmits on the supervisory channel a datasignal addressed to the now off-hook mobile set 8 which designates thetransmit and receive pseudo-random codes for the two-way voice channelto be used for voice communication to match those of the transmitter andreceiver. The mobile set adopts the codes and thus can transmit andreceive on the designated channel. Voice communication between thetelephone set 7 and mobile set 8 now proceeds on the specified channel,while using the dedicated supervisory channel for supervisory signals.

When either of the sets goes on hook at the conclusion of thecommunication, the supervisory signal associated with that function iscarried by the supervisory channel as described earlier during the setup of a call. The voice connection is then taken down in a manneranalogous to setting up all supervisory and voice or data communicationthus can proceed in this manner.

FIG. 1A illustrates the preferred form of channel assignments. Dedicatedpseudo-random codes designate the supervisory channel in each direction,while a plurality of pseudo-random codes (e.g. up to approximately40,000)can be used to designate the transmit and receive channels. Allchannels use essentially the same frequency band, though different bandsare used in the centre to mobile and mobile to centre directions. Nonewill be found to interfere with each other or with other wirelessservices using the same frequencies, except for random bit errors whichwill increase with traffic. In a typical system only about 32 two-waychannels will be required although there is clearly capacity for manymore, given the number of codes available.

In a similar manner calls can be made from any mobile set 8. All mobilesets 8 continuously receive and transmit information on the supervisorychannel. Thus if a mobile set 8 goes off-hook this information istransmitted by the supervisory channel to receiver 4 where it isdemodulated, despread and decoded before passing to PABX 5. On receivingthe off-hook signal PABX 5 allocates a voice channel as described above,transmits dial tone to the mobile set 8, receives signalling informationfrom mobile set 8 and sets up the call in the usual manner. The mobilesets 8 are clearly not limited to voice communications; they can becombination voice and data sets, or restricted to being data terminals.Inthis respect one of the trunks 6 of PABX 5 can be connected to acomputer for receiving data from and transmitting data to a mobile dataset 8. Alternatively a computer can be connected directly to the mainbus of PABX5 for communication with the mobile sets. In this manner themobile set 8 can be used as a remote terminal to a central computer Lowspeed data communication can be effected with the mobile set 8 via thesupervisory channel, or high speed via a dedicated data channel, or viaa voice channel shared with and carrying data.

Block diagrams of the mobile set and central equipment constituting thetransmitter and receiver are shown in FIGS. 2 and 3. The mobile set willbe described first, with reference to FIG. 2.

An analog telephone set 15 to which a handset or handset with display 16isconnected and, if desired, a keypad 17 has an internal hybrid with anoutput line connected to an analog-to-digital PCM encoder 18. Preferablythe encoder is an adaptive differential encoder of toll quality, e.g. itwill encode a signal which is output at 32 kb/sec.

The output of encoder 18 is connected to the input of modulator 19,which both spread spectrum and RF modules the incoming signal. Theoutput of modulator 19 is connected to the input of a combiner 21 whichis connectedthrough a transmit filter 22 and directional coupler 22A toan antenna 23.

The filter preferably is 8 megahertz wide, having a Q between 20 and100. It can for example be a printed strip line controlled by varacterdiodes such as is often found in the tuner of a TV set.

The antenna 23 is similarly connected through a directional coupler 23Ato the input of the receive filter 24 (which is similar to filter 22)which is connected to the input of a splitter 25. One output of splitter25 is connected to demodulator 27 which both spread spectrum and RFdemodulates the signal. The output of demodulator 27 is connected to theinput of digital-to-analog PCM decoder 28, the output of which isconnected to the input line to telephone 15.

A data interface circuit 29 is also connected to telephone set 15, whichcontains data encoding and signalling circuitry as well as associatedbuffers. Considering only the signalling aspect for the moment,off-hook, on-hook, etc. and other signalling signals as are normallygenerated in a telephone set are applied via interface circuit 29 to asynchronization and control circuit 30. The synchronization and controlcircuit contains amaster clock for the mobile set, and controls thefilters 22 and 24. The clock signal used in the synchronization andcontrol circuit is obtained from the incoming signal received viaantenna 23.

A spread spectrum and RF modulator 31 has its input connected tosynchronization and control circuit 30, and its output connected toanother input of combiner 21. The output of RF modulator 38 is connectedto another input of combiner 21.

A second output of splitter 25 is connected to an input of demodulator34, which has its output connected to synchronization and controlcircuit 30.

A voltage controlled oscillator circuit 35 is connected to thesynchronization and control circuit 30, and has outputs connected tomodulators 19, 31 and 38 and demodulators 27, 34 and 41.

Synchronization and control circuit 30 also has outputs connected tomodulators 19, 31 and 38 and demodulators 27, 34 and 41.

In operation, according to the preferred embodiment of the invention thepseudo-random codes designating the transmit and receive supervisorychannels are fixed by means of code plugs or other similar codedesignating means, fixed in modulator 31 and demodulator 34. Asupervisorysignal having a spreading code correlatable by thecorrelation code in demodulator 34 is received from the leaky cabletransmission line 2 (FIG. 1) by antenna 23. The signal passes throughdirectional coupler 22A, is filtered in filter 24, passes throughsplitter 25 and into demodulators 27and 34. However since demodulator 27will not recognize the encoded signal,it outputs only a low level randomnoise signal. However since spread spectrum modulator 34 does recognizethe supervisory channel code, it decodes the signal and applies it tosynchronization and control circuit 30. Synchronization and controlcircuit 30 recognizes a data header designating the local mobile set andfurther recognizes the demodulated code as meaning that ringing shouldstart. It applies a signal to telephone controller 15, which beginsringing. If the local mobile set data header was not recognized, theringing function would not be enabled.

It should be noted that on the supervisory channel the code which isreceived can designate any supervisory function or indeed can carry lowspeed data communication signals. In this respect it is preferred thatthesignal carried on this channel should contain four 8 bit words insequence:the first 8 bits designating the station number of the mobileset, and second 8 bits designating what function should be performed,the third 8 bits should contain bits to enable error detection andcorrection, and thefourth group of 8 bits should contain asynchronization pattern.

With the local telephone set going off-hook, telephone controller 15applies an off-hook signal to synchronization and control circuit 30.Synchronization and control circuit 30 in turn generates a code sequencecontaining the local station address identifier, a supervisory codedesignating "off hook", error correction bits and a synchronizationpattern and applies it to modulator 31. Modulator 31 modulates thesignal using the fixed supervisory channel code and also RF modulatesthe signal applied to it before applying it to an input of combiner 21.The output signal of combiner 21 is applied through filter 22 anddirectional coupler22A to antenna 23 from which it is transmitted toleaky cable transmission line 2.

A supervisory signal is also received from the central equipment in thesame manner as noted above which designates which channel or channelsthe incoming and outgoing analog and/or data signals from and to themobile set are to be transmitted. This channel designating signal isreceived by the synchronization and control circuit 30 over thesupervisory channel. The synchronization and control circuit 30 uponreceiving the channel designating signals applies signals to modulator19 and demodulator 27 which control the pseudo-random spreading andcorrelating codes respectively. Once these codes have been establishedin the modulator and demodulator, subsequent signals will be transmittedon a spread spectrum channel designated by the modulation pseudo-randomspreading code and received by the mobile set on a spread spectrumchannel designated by the designated correlation.

For transmission of analog or analog and data signals from the localhandset, such signals pass from handset 16 (and/or keypad 17) intotelephone 15 in the usual manner, are split into unidirectional signals,e.g. in a hybrid, and the outgoing signals are applied to PCM encoder18. The resulting digital output signals are applied to spread spectrummodulator 19, are modulated using the channel spreading code establishedtherein as described above, and are applied to RF modulator 20. Undercontrol of the synchronization and control circuit 30 modulator 20modulates the signal, and the resulting RF modulated spread spectrumsignal is applied via multiplexer 21 through filter 22 to antenna 23 fortransmission to the leaky cable transmission line.

A signal received from leaky cable transmission line 2 by antenna 23 isapplied through directional coupler 22A, filter 24, and splitter 25 todemodulators 27 and 34 which are controlled by synchronization andcontrolcircuit 30. The resulting demodulated and despread signal fromdemodulator 27 is applied to PCM decoder 28. The resulting analog outputsignal is applied to the incoming signal line of telephone 15 from whereit is applied to handset 16. However since demodulator 34 will notrecognize thepseudo random code used it will not apply any input tosynchronization and control circuit 30.

In the above manner all of the supervisory functions of the mobile setcan be received and transmitted, the analog signal receive and transmitchannels established and the analog and low speed data transmitted andreceived.

It is preferred that when no radio frequency signals are being received,decoder 28 should be switched into a silence mode. A silence codegenerator 36 is connected to the output of demodulator 27. When thesilence code generator 36 detects silence code at the output ofdemodulator 27, it applies a signal to decoder 28 which causes it toremain stable in a known state, whereby no analog output signal isgenerated.

Similarly, a silence detector 37 is connected to the outgoing signalline of telephone set 15 for detecting silence. The output of silencedetector 37 is applied to synchronization and control circuit 30, whichreduces or shuts off modulator 19 for that interval. This results in areduced error rate of signals received by the central system andreproduced in the mobile set. The silence code detector 28 and silencedetector 37 should bevery fast acting so as to prevent the clipping ofthe start of words. Silence detectors have been used in TASI (timeassignment speech interpolation) transmission systems.

In order to transmit and receive high speed data, data interface circuit29interfaces via telephone 15 to the display in the display and handset16 and to the keypad 17, or to an external port (not shown) which mayreceivedata from a local data collection machine or the like. The highspeed data is applied through data interface 29 to modulator 38 ofconstruction similar to that of modulator 19. The output of modulator 38is connected to an input of combiner 21.

An output of splitter 25 is connected to an input of demodulator 41,which has its output connected to the incoming data port of datainterface 29.

For reception and transmission of data, modulator 38 and demodulator 41operate similarly to modulator 19 and demodulator 27 respectively. Themodulator 38 and demodulator 41 are controlled upon receipt of a signalinthe synchronization and control channel designating that data is to bereceived or transmitted, in a manner similar to that described earlier.Channels are designated by the allocation of pseudo-random codes asdescribed earlier. The data can be transmitted using simple packets at90.2 Kilobits per second, for example, the packets containing datasignalsand error correction codes.

Turning now to FIG. 3, the transmitter and receiver and PABX interfaceat the central equipment are illustrated. The elements in thetransmitter andreceiver referred to with respect to FIG. 1 will becomeevident by the description below and have not been segregated, for thepurpose of clarityof explanation.

A PABX 5 includes a plurality of interface circuits 42, one of which isshown. Each interface circuit can be similar to a well known PABX linecircuit except that it has an additional communication link with themain bus of the PABX for receiving synchronization pulses fortransmission to the mobile set.

When a telephone set 7 wishes to communicate with a mobile set, forexample, a subscriber will dial digits designative of the particularmobile set to be contacted. The PABX, in the normal manner, can select aline terminal or port which is unique to that mobile set. However use ofthe system in this manner would require as many line circuits orterminations as there are mobile sets. It is preferred, instead, to havethe PABX select a particular junctor with a PABX interface connectedthereto, with the mobile set to be selected designated by address orground point. Use of the system in this preferred manner will requireonlyas many interface circuits as the traffic requires, clearly aconsiderably fewer number of interfaces, circuits and channels than thenumber of mobile sets.

With the interface selected and either a line termination enabled or adatacode received from the PABX which designates the mobile set to berung, a sync and control circuit 43 receives both the supervisory signaland designation of the mobile set to be contacted from the PABX via thePABX interface. The sync and control circuit 43 formulates a data packetcomprised of the station number, supervisory signal, error correctionand synchronization pattern bits and transmits it to a modulator 44.Modulator44 has a dedicated pseudo-random spreading code fixed to thesupervisory channel. The modulator 44 spread spectrum and RF modulatesthe supervisorysignal (which in this case contains a supervisorysequence which indicates that a particular mobile set should be rung).The modulated output signal therefrom is applied to multiplexer 46 fromwhich it is passed to 8 megahertz filter 47, which is similar to filter22. The output signal of filter 47 is applied to one end of leakytransmission cable 2. The signal passes along transmission cable 2,radiating as described earlier. The radiated signal is received bymobile set 8 in the manner described above.

A signal received from the mobile set 8 passes through 8 megahertzfilter 48 (which is similar to filter 47) and splitter 49 anddemodulator 51. Since the supervisory signal is on a fixed channel, thepseudo-random correlation code for demodulator 51 is fixed, and thereceived signal is demodulated resulting in a data signal applied tosync and control circuit43 which constitutes the return supervisorysignal (e.g. an off hook indication) from mobile set 8. Sync and controlcircuit 43 applies this signal to PABX interface 42 which applies it inrecognizable form to PABX 5.

Sync and control circuit 43 also has outputs connected to modulators 44,53and 59 and demodulators 51, 56 and 62 for applying a synchronizationand control signals thereto.

Since a particular junctor, and thus PABX interface 42 was selected bythe PABX for the forthcoming communication, the particular outgoing andincoming channels are thereby designated, and a mark signal related totheparticular channels is applied to sync and control circuit 43. Syncand control circuit 43 contains a table of pseudo-random codescorresponding to the selected spread spectrum modulator and demodulator,and another table of mobile set station numbers corresponding to themark signal (which identifies the caller mobile station uniquely. Asupervisory signalis formulated in sync and control circuit 43, which issent to the selectedmobile set 8 identified by station number, advisingit what spread spectrumchannel to tune itself to.

The supervisory signal can send to the mobile set one of two kinds ofsignals: a signal advising the mobile set to establish its receive andtransmit spread spectrum modulator and demodulator pseudo-random codesto codes stored in a table in each mobile set, i.e. identifying thecodes by number. Alternatively the sync and control circuit can transmitthe actualpseudo-random codes to the selected mobile set 8 to enable itto set its modulator and demodulator to the designated spread spectrumchannels In this manner, in a 200 mobile set system, typically 32junctors and thus 32PABX interfaces can be used, rather than 200interfaces would be required if each line circuit were separatelyinterfaced. However the present invention contemplates the use ofindividual line circuits for each two-way channel if economics dictate.

Since a particular junctor, and thus a particular PABX interface circuit42has been selected by the PABX in the normal manner to carry thecommunication, the outgoing and incoming channels are also fixed asnoted above. The output signal from the PABX interface circuit isapplied to analog digital PCM encoder 52. The resulting encoded outputsignal is applied to the input of modulator 53 which has a dedicatedpseudo-random code related to that particular channel. The RF modulatedoutput signal isapplied to an input of combiner 46, from which it passesthrough filter 47 and is applied to the leaky cable 2. Since the spreadspectrum modulation codes in modulator 53 and modulator 44 aredifferent, there will be no interference between the two signals. Thesignal applied to leaky cable 2 is radiated for reception by mobile sets8 as described earlier.

A received signal from the leaky cable 2 transmitted by mobile set 8passesthrough filter 48 and combiner 49, is demodulated and despread indemodulator 56, and the resulting signal is passed to analog PCM decoder57. The resulting output signal is applied to PABX interface 42 forapplication to the junctor of PABX 5. Since the spread spectrumpseudo-random spreading code at the mobile set for signals transmittedthereat under control of sync and control circuit 43, were designated bythe selection of a particular junctor and PABX interface circuit 42 bynormal operation of the PABX, which is identical to that pseudo-randomcode in spread spectrum demodulator 56, the signal received from mobileset 8 is properly decoded in demodulator 56, but is rejected bydemodulator 51.

The PABX interface can also interface to high speed data junctors, or toa data bus in the PABX which designates by code which mobile set is tobe communicated with. Either by junctor selection as described above orby decoded selection from the PABX data bus, the high speed data signalis applied to outgoing data interface circuit 58. The output signal isapplied to modulator 59, in a manner analogous to that describedearlier. The RF modulated signal is applied to an input of combiner 46,passes through filter 47 and is applied to the leaky cable 2.

Received high speed data signals from mobile set 8 are received by leakycable 2 and pass through filter 48, splitter 49 and are applied todemodulator 62. The resulting data output signal after spread spectrumandRF demodulation is applied to data interface circuit 63, from whichthe data signal is applied to the junctor or data bus of the PABXthrough PABXinterface circuit 42. The data channel selection at themobile set 8 is established as the incoming and outgoing data channelsin a manner analogous to that described above for the outgoing andincoming analog channel.

It is preferred that a silence detector and a silence code detectorshould be used in each of the incoming and outgoing analog channels ofthe central equipment (not shown) which are similar to those describedwith reference to FIG. 2 and are similarly connected. The silence andsilence code detectors should be very fast acting. Since the error ratesof the signals which are received are dependent on the total number ofchannels sharing the same bandwidth, it is highly desirable to switchthe RF or IF signals off or to extremely low level during silentperiods. For a given error rate, the use of silence detectors willincrease the number of channels which can share the same bandwidth atthe same time. Synchronization will not be lost since the supervisorychannel will alwaysbe operating and carries synchronization signals.Thus the receivers at themobile sets and at the central equipment canalways regain synchronization if it is lost.

When communication has been set up the mobile sets thus each will havetwo receive addresses, one which is a polling address which is used onthe synchronization channel and the other which is the pseudo-randomcode, i.e. the correlation code that it is instructed to use via thesupervisorychannel. It will use two transmit addresses, one whichdesignates it and allows it to be recognized in the supervisory receivechannel at the central equipment and one a pseudo-random code whichmatches the analog ordigital receive channel code at the centralequipment. Thus the instructionto use a particular correlation code issimilar to the designation to the mobile set to use a particularjunctor, and is directly analogous to the junctor selected at the PABX.It can additionally have separate high speeddata channel receive andtransmit spreading and correlation code addresses.

The pulse code modulation scheme which is used is preferred to beadaptive differential PCM, a full description of which can be obtainedin the draftrecommendation G721 of CCITT. According to thisspecification PCM is transcoded from 64 Kilobits per second to 32Kilobits per second. It is also preferred that the pseudo noise codesequence used in the spread spectrum modulator should be 255 bits,although it is expected that other sequence lengths could be used. It isalso preferred that the RF modulation should be phase shift keyed, andcan be minimum shift keyed, bandwidth phase shift keyed, QPSK orstaggered phase shift keyed. It is also preferred that the data channelsshould transmit at 90.2 kilobits persecond.

It should be noted that only one sync and supervisory channel modulatoranddemodulator 44 and 51 need be used for the entire system while thePABX interface and decoders, modulators and demodulators are duplicatedfor each channel. Of course apparatus used for the data, or for theanalog channels need not be used if one or the other kind ofcommunication is notto be provided for a particular junctor or forcommunication to the mobile sets in general.

Referring now to FIG. 4, the modulation portion of the transmitter isshown. An incoming PCM or data signal from encoder 52, for example, iscarried on line 64 to a data circuit 65, in which the incoming signal issynchronized and speed adjusted. The outgoing signal from data circuit65 is applied to an exclusive OR gate 66. A sequence generator 67generates apseudo-random code which is specific to the channel to betransmitted and applies its output to another input of exclusive OR gate66. One complete pseudo-random code, of preferred length 255 bits, isExclusively ORed witheach data bit. The resulting PN sequence ofexclusive OR gate 66 is appliedto an input of data modulator 68. Thedata circuit 65, sequence generator 67 and exclusive OR gate 66 providesthe spread spectrum modulation.

An intermediate frequency (IF) oscillator 69 generates a signal which isapplied to data modulator 68, where it modulates the signal, resultingin a IF signal on line 70. The IF signal is applied to a summer 71,along with the IF signals of other data modulators, illustrated byline71A. The output signal of summer 71 is applied to a mixer 72, to whichis applied an RF carrier signal generated in a carrier generator 73. Thecarrier signal is mixed with the sum IF signal and the resulting RFmodulated output signal of mixer 72 is applied to an 8 megahertz filter74. The output filter of signal 74 is applied to leaky transmission line2.

It is preferred that the data modulator should modulate the IF signalwith the output of Exclusive OR gate 66 using phase shift modulation.

It will be noted that in the circuit of FIG. 4 the modulated signalshave been summed prior to RF modulation in mixer 72. The summer 71 is ofcourseequivalent to combiner 46. The IF signals can be summed prior toRF modulation as shown in FIG. 4, or the RF signals can be summedfollowing RF modulation as shown in FIG. 3.

The receive channel is similar to FIG. 4 in that the mixer outputs to asplitter the IF signal in a well known manner and the resulting signalis applied to a data demodulator. The demodulator multiplies theincoming signal by an IF signal modulated by the same pseudo-random codeused in the transmitter. The output of the demodulator is then low-passfiltered to recover the data.

While the circuit of FIG. 4 can be used in the transmit and receivechannels of the central equipment shown in FIG. 3, the major differentbetween that circuit and the circuit used in mobile set 8 is that thesequence generator can generate a selected code sequence in the latter.Asnoted earlier the sequence is established either by a look up table inthe mobile set which is designated by the supervisory signal receivedfrom thecentral equipment or by reception of the actual sequence to beused. Of course the receive channel is directly analogous to thetransmit channel.

Returning to the supervisory channel, during idle intervals it ispreferredthat the central equipment should transmit a 32 bit supervisorypolling message to each mobile set in sequence and to wait for aresponse in the following 32 bit message. In case erroneous messages arereceived, it is preferred that a request for a repetition should betransmitted in the next supervisory sequence designated for theparticular mobile set or the particular junctor channel time period. Inthe analog and data channels either repetition or error correction, orignoring packets which have beendesignated as erroneous can beimplemented. Since the supervisory channel operates by polling,transmission collisions are avoided.

Each of the elements described above can be implemented in dedicatedlogic to provide the functions described, or can be grouped andimplemented in microprocessor-memory combinations operated usingfirmware written using the algorithms described herein.

Since radiation from a leaky transmission cable is used, extremely lowpowers can be used, e.g. ten milliwatts per channel. Clearly the powerused in the mobile sets, typically operated by battery, is greatlyeconomized.

Since spread spectrum is used in combination with the leaky cables,nulls which are usually encountered using leaky feeder systems, andsignal dropout regions often encountered using fixed antenna radiatorsare substantially avoided. Since there is a fast drop off of signallevel withdistance from the leaky cable radiator, the judiciousplacement of leaky cable in the ceiling or other peripheral region ofthe building will establish detectable power levels throughout thebuilding, but virtually undetectable RF signals outside of the environsof the building. Thus the system is highly localized, minimizing anyinterference with any other kinds of systems.

Further, because the system is spread spectrum, it is inherentlyprivate, which is highly unusual in a wireless telephone system. It iseconomical of spectrum space, since substantially the same bandwidth isused for all channels. With the very low level of power which is used,and each channelbeing spread over a wide bandwidth, the actualtransmitted signal appears to be little more than very low level noiseto conventional wireless systems. Yet because there are such a greatnumber of pseudo random codes which can be used, the possibility ofinterference between channels, or ofinterception outside of the presentsystem is rendered almost nil.

The system can be used for conventional analog voice communication, asnoted earlier, or in addition or in alternative the mobile set can be ahand held computer terminal. However since each mobile set can transmitoneither a designated or centrally controlled secure channel, the mobileset can also be used for remote control of apparatus such as automaticdoors, various building services, etc. with high security. For exampleit can control robots, domestic appliances, etc. The mobile set is thusa highly versatile unit used in conjunction with the system describedabove.

It should also be noted that while the modulators and demodulators atthe central equipment have fixed pseudo random codes and those at themobile sets have codes which are variable, in an alternative system thecodes at the mobile sets can be fixed, and the codes at the centralequipment can be varied to select a channel corresponding to thedesignated mobile set. However in this case the number of variablepseudo-random cOdes which are used will correspond to twice the numberof mobile sets (two one-way channels to each mobile set), plus two forsupervisory while in the case in which the mobile sets change theircorrelation codes, the number of correlation codes used will correspondto twice the number of junctors or total channels expected to be usedfor communication (plus two for supervisory), a far fewer number.

Further, the central apparatus described herein could usefully beemployed to operate with one or a group of distributed antennae, ratherthan, or inaddition to, the leaky cable. Such a structure would findgreat utility in buildings or outdoor areas in which it is not feasibleto wire telephone system connected by wires, or to deploy a leaky cable.

A person understanding this invention may now conceive of variousalternative structures using the principles described herein. All areconsidered to be within the scope of the invention as defined in theclaims appended hereto.

We claim:
 1. A wireless system for telephone communication within abuilding comprising:(a) means at a central location for receiving aplurality of signals for communication with selected wirelesscommunication terminals, (b) means at said central location forconverting said signals to spread spectrum radio frequency signals usingcorrelation codes corresponding to particular idle channels, (c) a leakytransmission line located in a communication region within the building,(d) means for applying said spread spectrum radio frequency signals tosaid transmission line for electromagnetic radiation within said region,(e) at least one mobile wireless communication terminal adapted toreceive a predetermined one of the spread spectrum radio frequencysignals within the building and for demodulating it into an intelligiblesignal, and (f) a plurality of similar circuits each comprising aninterface means at the central location for connection to an individualjunctor of a PABX, for receiving and transmitting communication signalsfrom said junctor and for receiving and transmitting communicationsignals from said junctor and for receiving and transmitting supervisorysignal from the PABX relating to a telephone call, a central PCM encoderconnected to the interface means for receiving signal to be transmittedto a wireless communication terminal, a modulator using a fixedpseudo-random correlation code associated with the junctor for spreadspectrum modulating the encoded signal and generating an RF modulatedsignal, means for applying the latter RF modulated signal through atransmit band limiting filter to the leaky transmission line, means forreceiving an RF modulated signal from the leaky transmission linethrough a receive band limiting filter, a central RF demodulator fordemodulating and despreading a received RF modulated signal using afixed pseudo-random correlation code associated with said junctor fordemodulating the latter signal, a PCM decoder for receiving a spreadspectrum demodulated signal and applying it to the interface means forapplication to said junctor, a central synchronization and controlcircuit connected to all said interface means for receiving supervisorysignal from the junctors and/or a bus of the PABX and for formulatingpolling and supervisory signal of predetermined format received from thewireless communication terminal corresponding thereto and fortranslating poll messages and supervisory signal of predefined format tosupervisory signal and for applying the latter signal to the junctorsand/or bus of the PABX, a supervisory channel spread spectrum modulatorusing a predetermined supervisory channel correlation code for receivingand spread spectrum modulating said formulated polling and supervisorysignal, RF modulating the latter signal and applying the RF modulatedsignal via the transmit band limiting filter to the leaky transmissionline, a supervisory channel demodulator connected to the output of thereceive band limiting filter for RF demodulating and despreading areceived signal and applying received poll and supervisory signals tothe synchronization and control circuit.
 2. A system as defined in claim1 including means for transmitting a supervisory signal on a fixedspread spectrum supervisory channel to said wireless communicationterminal, means at said terminal for receiving a predetermined form ofsaid supervisory signal designative of a particular correlation coderelated to a receive channel, and means for correlating thepredetermined one of the spread spectrum signals using the correlationcode to effect said demodulation into said intelligible signal.
 3. Asystem as defined in claim 1 including means at the central location forreceiving a signal at a particular port designative of a particularjunctor or channel of an incoming signal, and means for transmittingsaid spread spectrum supervisory signal to said wireless terminalcontaining said predetermined form of said supervisory signaldesignative of said particular correlation code corresponding to saidparticular junctor or channel.
 4. A system as defined in claim 1including means at the central location for transmitting said spreadspectrum communication signals to the wireless communication terminalsusing pseudo-random spreading codes which correspond to predeterminedfixed correlation codes associated with individual ones of the wirelesscommunication terminals.
 5. A system as defined in claim 1, in whicheach wireless communication terminals is comprised of:(i) a telephoneset, (ii) means for PCM encoding signals received from the telephoneset, (iii) means for spread spectrum and RF modulating the PCM encodedsignals using a first pseudo-random correlation code, (iv) means forapplying the RF modulated signals to an antenna through a first filterfor wireless transmission to the leaky transmission line, (v) means forreceiving RF and spread spectrum modulated signals from the antenna viaa second filter, (vi) means for receiving RF and spread spectrumdemodulating the received signals using a second pseudo-randomcorrelation code different from the first correlation code, (vii) meansfor PCM decoding the spread spectrum demodulated signals, (viii) meansfor applying the PCM decoded signals to the telephone, whereby wirelesstwo-way communication via said leaky transmission line on channelsdesignated by the correlation codes is provided.
 6. A system as definedin claim 5 in which the first and second correlation codes are variable,and means for causing variation thereof whereby particular designatedsend and receive spread spectrum channels are established.
 7. A systemas defined in claim 6 including a synchronization and control circuit, asecond demodulator having its input connected to the output of saidsecond filter for receiving a supervisory signal includingsynchronization signals, and providing demodulated digital supervisorysignals therefrom to the synchronization and control circuit, the seconddemodulator using a fixed predetermined correlation code fordemodulation of the supervisory signals, a second modulator having itsinput connected to the synchronization and control circuit for receivingsupervisory signals and spread spectrum modulating said latter signalsusing a fixed predetermined pseudo-random code different from that ofthe correlation code used in the first modulator, RF modulating thesesignals and applying the signals via the second filter to the antenna,and means in the synchronization and control circuit for receivingsupervisory signals from the telephone, generating supervisory datasignals of predefined format and applying them to the second modulator,and for receiving supervisory data signals of predefined format from thesecond demodulator, for translating said latter supervisory signalstherefrom and applying said translated signals to the telephone.
 8. Asystem as defined in claim 7 including means at the synchronization andcontrol circuit for deriving designated correlation codes from thereceived supervisory signals of predefined format and for enabling thefirst modulator and demodulator to use said latter correlation codes inmodulation and demodulation respectively to establish the receive andtransmit channels for said signals.
 9. A system as defined in claim 8including means for generating and displaying data at said wirelesscommunication terminal, a data interface circuit connected to said datagenerating and displaying means, third means for spread spectrum and RFmodulating data signals received via said interface circuit and applyingthe RF modulated signals to the first filter for transmission via theantenna to the leaky transmission line, third demodulation means havingits input connected to the antenna via the second filter, and its outputconnected to the data interface circuit for applying demodulated datasignals thereto, and means connecting the third modulator anddemodulator to the synchronization and control circuit for carryingsignals therefrom designative of the pseudo-random correlation codes tobe used by the third modulator and demodulator.
 10. A wirelesscommunication system comprising:(a) means at a central location forreceiving a plurality of signals for communication with selectedwireless communication terminals, (b) means at said central location forconverting said signals to spread spectrum radio frequency signals usingcorrelation codes corresponding to particular idle channels, (c) a leakytransmission line located in a communication region within the building,(d) means for applying said spread spectrum radio frequency signals tosaid transmission line for electromagnetic radiation within said region,(e) at least one wireless communication terminal adapted to receive apredetermined one of the spread spectrum radio frequency signals and fordemodulating it into an intelligible signal, and (f) a plurality ofsimilar circuits each comprising an interface means at the centrallocation for connection to an individual junctor of a PABX, forreceiving and transmitting communication signals from said junctor andfor receiving and transmitting supervisory signals from the PABXrelating to a telephone call, a central PCM encoder connected to theinterface means for receiving signals to be transmitted to a wirelesscommunication terminal, a modulator using a fixed pseudo-randomcorrelation code associated with the junctor for spread spectrummodulating the encoded signal and generating an RF modulated signal,means for applying the latter RF modulated signal through a transmitband limiting filter to the leaky transmission line, means for receivingan RF modulated signal from the leaky transmission line through areceive band limiting filter, a central demodulator for demodulating anddespreading a received RF modulated signal using a fixed pseudo-randomcorrelation code associated with said junctor for demodulating thelatter signal, a PCM decoder for receiving a spread spectrum demodulatedsignal and applying it to the interface means for application to saidjunctor, a central synchronization and control circuit connected to allsaid interface means for receiving supervisory signals from the junctorsand/or a bus of the PABX and for formulating polling and supervisorysignals of predefined format corresponding thereto and for translatingpoll messages and supervisory signals of predefined format tosupervisory signals and for applying the latter signals to the junctorsand/or bus of a the PABX, a supervisory channel correlation code forreceiving and spread spectrum modulating said formulated polling andsupervisory signals, RF modulating the latter signal and applying the RFmodulated signal via the transmit band limiting filter to the leakytransmission line, a supervisory channel demodulator connected to theoutput of the receive band limiting filter for RF demodulating anddespreading a received signal and applying received poll and supervisorysignals to the synchronization and control circuit, a plurality ofunidirectional repeaters connected serially at spaced locations in theleaky transmission line whereby an input and an output to the line aredefined, the transmit filter being connected to the input of thetransmission line and the receive filter being connected to the outputof the transmission line.
 11. A system as defined in claim 10, in whicheach wireless communication terminal is comprised of:(i) a telephoneset, (ii) means for PCM encoding signals received from the telephoneset, (iii) means for spread spectrum and RF modulating the PCM encodedsignals using a first pseudo-random correlation code, (iv) means forapplying the RF modulated signals to an antenna through a first filterfor wireless transmission to the leaky transmission line, (v) means forRF and spread spectrum modulated signals from the antenna via a secondfilter, (vi) means for RF and spread spectrum demodulating the receivedsignals using a second pseudo-random correlation code different from thefirst correlation code, (vii) means for PCM decoding the spread spectrumdemodulated signals, (viii) means for applying the PCM decoded signalsto the telephone, whereby wireless two-way communication via said leakytransmission line on channels designated by the correlation codes isprovided.
 12. A system as defined in claim 11 in which the first andsecond correlation codes are variable, and means for causing variationthereof whereby particular designated send and receive spread spectrumchannels are established.
 13. A system as defined in claim 12 includinga synchronization and control circuit, a second demodulator having itsinput connected to the output of said second filter for receiving asupervisory signal including synchronization signals, and providingdemodulated digital supervisory signals therefrom to the synchronizationand control circuit, the second demodulator using a fixed predeterminedcorrelation code for demodulation of the supervisory signals, a secondmodulator having its input connected to the synchronization and controlcircuit for receiving supervisory signals and spread spectrum modulatingsaid latter signals using a fixed predetermined pseudo-random codedifferent from that of the correlation code used in the first modulator,RF modulating these signals and applying the signals via the secondfilter to the antenna, and means in the synchronization and controlcircuit for receiving supervisory signals from the telephone, generatingsupervisory data signals of predefined format and applying them to thesecond modulator, and for receiving supervisory data signals ofpredefined format from the second demodulator, for translating saidlatter supervisory signals therefrom and applying said translatedsignals to the telephone.
 14. A system as defined in claim 13 includingmeans at the synchronization and control circuit for deriving designatedcorreleation codes from the received supervisory signals of predefinedformat and for enabling the first modulator and demodulator to use saidlatter correlation codes in modulation and demodulation respectively toestablish the receive and transmit channels for said signals.
 15. Asystem as defined in claim 14 including means for generating anddisplaying data at said wireless communication terminal, a datainterface circuit connected to said data generating and displayingmeans, third means for spread spectrum and RF modulating data signalsreceived via said interface circuit and applying the RF modulatedsignals to the first filter for transmission via the antenna to theleaky transmission line, third demodulation means having its inputconnected to the antenna via the second filter, and its output connectedto the data interface circuit for applying demodulated data signalsthereto, and means connected the third modulator and demodulator to thesynchronization and control circuit for carrying signals therefromdesignative of the pseudo-random correlation codes to be used by thethird modulator and demodulator.
 16. A wireless communication systemcomprising:(a) means at a central location for receiving a plurality ofsignals for communication with selected wireless communicationterminals, (b) means at said central location for converting saidsignals to spread spectrum radio frequency signals using correlationcodes corresponding to particular idle channels, (c) a leakytransmission line located in a communication region within the building,(d) means for applying said spread spectrum radio frequency signals tosaid transmission line for electromagnetic radiation within said region,(e) at least one mobile wireless communication terminal adapted toreceive a predetermined one of the spread spectrum radio frequencysignals and for demodulating it into an intelligible signal, and (f) aplurality of similar circuits each comprising an interface means at thecentral location for connection to an individual junctor of a PABX, forreceiving and transmitting communication signals from said junctor andfor receiving and transmitting supervisory signals from the PABXrelating to a telephone call, a central PCM encoder connected to theinterface means for receiving signals to be transmitted to a wirelesscommunication terminal, a modulator using a fixed pseudo-randomcorrelation code associated with the junctor for spread spectrummodulating the encoded signal and generating an RF modulated signal,means for applying the latter RF modulated signal through a transmitband limiting filter to the leaky transmission line, means for receivingan RF modulated signal from the leaky transmission line through areceive band limiting filter, a central demodulator for demodulating anddespreading a received RF modulated signal using a fixed pseudo-randomcorrelation code associated with said junctor for demodulating thelatter signal, a PCM decoder for receiving a spread spectrum demodulatedsignal and applying it to the interface means for application to saidjunctor, a data interface circuit connected to the former interfacecircuit for receiving and transmitting data signals from and to theassociated junctor and/or data bus of the PABX, a data channel modulatorhaving a fixed correlation code corresponding to the junctor connectedto the data interface circuit for spread spectrum and RF modulating adata signal received therefrom and applying the RF modulating signal viathe transmit filter to the leaky transmission line, a data channeldemodulator having its input connected via the receiver filter to theleaky transmission line, and for applying a data signal to the datainterface circuit for transmission to the junctor or PABX data bus, acentral synchronization and control circuit connected to all saidinterface means for receiving supervisory signals from the junctorsand/or bus of the PABX and for formulating polling and supervisorysignals of predefined format received from the wireless communicationterminal corresponding thereto and for translating poll messages andsupervisory signals of predefined format to supervisory signals and forapplying the latter signals to the junctors and/or bus of the PABX, asupervisory channel modulator using a predetermined supervisory channelcorrelation code for receiving and spread spectrum modulating saidformulated polling and supervisory signals, RF modulating the lattersignal and applying the RF modulated signal via the transmit bandlimiting filter to the leaky transmission line, a supervisory channeldemodulator connected to the output of the receive band limiting filterfor RF demodulating and despreading a received signal and applyingreceived poll and supervisory signals to the synchronization and controlcircuit.
 17. A wireless communication system comprising:(a) means at acentral location for receiving a plurality of signals for communicationwith selected wireless communication terminals, (b) means at saidcentral location for converting said signals to spread spectrum radiofrequency signals using correlation codes corresponding to particularidle channels, (c) a leaky transmission line located in a communicationregion within the building, (d) means for applying said spread spectrumradio frequency signals to said transmission line for electromagneticradiation within said region, (e) at least one wireless communicationterminal adapted to receive a predetermined one of the spread spectrumradio frequency signals and for demodulating it into an intelligiblesignal, and (f) a plurality of similar circuits each comprising aninterface means at the central location for connection to an individualjunctor of a PABX, for receiving and transmitting communication signalsfrom said junctor and for receiving and transmitting supervisory signalsfrom the PABX relating to a telephone call, a central PCM encoderconnected to the interface means for receiving signals to be transmittedto a wireless communication terminal, a modulator using a fixedpseudo-random correlation code associated with the junctor for spreadspectrum modulating the encoded signal and generating an RF modulatedsignal, means for applying the latter RF modulated signal through atransmit band limiting filter to the leaky transmission line, means forreceiving an RF modulated signal from the leaky transmission linethrough a receive band limiting filter, a central demodulator fordemodulating and despreading a received RF modulated signal using afixed pseudo-random correlation code associated with said junctor fordemodulating the latter signal, a PCM decoder for receiving a spreadspectrum demodulated signal and applying it to the interface means forapplication to said junctor, a central synchronization and controlcircuit connected to all said interface means for receiving supervisorysignals from the junctors and/or a bus of the PABX and for formulatingpolling and supervisory signals of predetermined format correspondingthereto and for translating poll messages and supervisory signals ofpredefined format to supervisory signals and for applying the lattersignals to the junctors and/or bus of a the PABX, a supervisory channelcorrelation code for receiving and spread spectrum modulating saidformulated polling and supervisory signals, RF modulating the lattersignal and applying the RF modulated signal via the transmit bandlimiting filter to the leaky transmission line, a supervisory channel RFdemodulator connected to the output of the receive band demodulatorconnected to the output of the receive bank limiting filter for RFdemodulating and despreading a received signal and applying receivedpoll and supervisory signals to the synchronization and control circuit,a plurality of unidirectional repeaters connected serially at spacedlocations in the leaky transmission line whereby an input and an outputto the line are defined, the transmit filter being connected to theinput of the transmission line and the receive filter being connected tothe output of the transmission line, the frequency of the R.F. modulatedsignals being between approximately 150 MHz and 1000 MHZ.
 18. A wirelesscommunication system comprising:(a) means at a central location forreceiving a plurality of signals for communication with selectedwireless communication terminals, (b) means at said central location forconverting said signals to spread spectrum radio frequency signals usingcorrelation codes corresponding to particular idle channels, (c) a leakytransmission line located in a communication region within the building,(d) means for applying said spread spectrum radio frequency signals tosaid transmission line for electromagnetic radiation within said region,(e) at least one mobile wireless communication terminal adapted toreceive a predetermined one of the spread spectrum radio frequencysignals and for demodulating it into an intelligible signal, and (f) aplurality of similar circuits each comprising an interface means at thecentral location for connection to an individual junctor of a PABX, forreceiving and transmitting communication signals from said junctor andfor receiving and transmitting supervisory signals from the PABXrelating to a telephone call, a central PCM encoder connected to theinterface means for receiving signals to be transmitted to a wirelesscommunication terminal, a modulator using a fixed pseudo-randomcorrelation code associated with the junctor for spread spectrummodulating the encoded signal and generating an RF modulated signal,means for applying the latter RF modulated signal through a transmitband limiting filter to the leaky transmission line, means for receivingan RF modulated signal from the leaky transmission line through areceive band limiting filter, a central demodulator for demodulating anddespreading a received RF modulated signal using a fixed pseudo-randomcorrelation code associated with said junctor for demodulating thelatter signal, a PCM decoder for receiving a spread spectrum demodulatedsignal and applying it to the interface means for application to saidjunctor, a central synchronization and control circuit connected to allsaid interface means for receiving supervisory signals from the junctorsand/or a bus of the PABX and for formulating polling and supervisorysignals of predetermined format corresponding thereto and fortranslating poll messages and supervisory signals of predefined formatto supervisory signals and for applying the latter signals to thejunctors and/or bus of a the PABX, a supervisory channel correlationcode for receiving and spread spectrum modulating said formulatedpolling and supervisory signals, RF modulating the latter signal andapplying the RF modulated signal via the transmit band limiting filterto the leaky transmission line, a supervisory channel demodulatorconnected to the output of the receive band limiting filter for RFdemodulating and despreading a received signal and applying receivedpoll and supervisory signals to the synchronization and control circuit,a plurality of unidirectional repeaters connected serially at spacedlocations in the leaky transmission line whereby an input and an outputto the line are defined, the transmit filter being connected to theinput of the transmission line and the receive filter being connected tothe output of the transmission line, the frequency of the RF modulatedsignals being between approximately 150 MHz and 1000 MHZ, thetransmission line being coaxial cable having a shield containing gapssufficient to allow RF energy radiation therefrom.
 19. A wirelesscommunication system comprising:(a) means at a central location forreceiving a plurality of signals for communication with selectedwireless communication terminals, (b) means at said central location forconverting said signals to spread spectrum radio frequency signals usingcorrelation codes corresponding to particular idle channels, (c) a leakytransmission line located in a communication region within the building,(d) means for applying said spread spectrum radio frequency signals tosaid transmission line for electromagnetic radiation within said region,(e) at least one mobile wireless communication terminal adapted toreceive a predetermined one of the spread spectrum radio frequencysignals within the building and for demodulating it into an intelligiblesignal, and (f) a plurality of similar circuits each comprising aninterface means at the central location for connection to an individualjunctor of a PABX, for receiving and transmitting communication signalsfrom said junctor and for receiving and transmitting supervisory signalsfrom the PABX relating to a telephone call, a central PCM encoderconnected to the interface means for receiving signals to be transmittedto a wireless communication terminal, a modulator using a fixedpseudo-random correlation code associated with the junctor for spreadspectrum modulating the encoded signal and generating an RF modulatedsignal, means for applying the latter RF modulated signal through atransmit band limiting filter to the leaky transmission line, means forreceiving an RF modulated signal from the leaky transmission linethrough a receive band limiting filter, a central demodulator fordemodulating and despreading a received RF modulated signal using afixed pseudo-random correlation code associated with said junctor fordemodulating the latter signal, a PCM decoder for receiving a spreadspectrum demodulated signal and applying it to the interface means forapplication to said junctor, a data interface circuit connected to theformer interface circuit for receiving and transmitting data signalsfrom and to the associated junctor and/or data bus of the PABX, a datachannel spectrum modulator having a fixed correlation code correspondingto the junctor connected to the data interface circuit for spreadspectrum and RF modulating a data signal received therefrom and applyingthe RF modulated signal via the receive band limiting filter to theleaky transmission line, a data channel demodulator having its inputconnected via the receive band limiting filter to the leaky transmissionline and for applying a data signal to the data interface circuit fortransmission to the junctor or PABX data bus, a central synchronizationand control circuit connected to all said interface means for receivingsupervisory signals from the junctors and/or a bus of the PABX and forformulating polling and supervisory signals of predefined formatcorresponding thereto and for translating poll messages and supervisorysignals of predefined format to supervisory signals and for applying thelatter signals to the junctors and/or bus of the PABX, a supervisorychannel modulator using a predetermined supervisory channel correlationcode for receiving and spread spectrum modulating said formulatedpolling and supervisory signals, RF modulating the latter signal andapplying the RF modulated signal via the transmit band limiting filterto the leaky transmission line, a supervisory channel demodulatorconnected to the output of the receive band limiting filter for RFdemodulating and despreading a received signal, and applying receivedpoll and supervisory signals to the synchronization and control circuit,a plurality of unidirectional repeaters connected serially at spacedlocations in the leaky transmission line whereby an input and an outputto the line are defined, the output of the transmit band limiting filterbeing connected to the input of the transmission line and the input tothe receive band limiting filter being connected to the output of thetransmission line.
 20. A system as defined in claim 19, in which eachwireless communication terminal is comprised of:(i) a telephone set,(ii) means for PCM encoding signals received from the telephone set,(iii) means for spread spectrum and RF modulating the PCM encodedsignals using a first pseudo-random correlation code, (iv) means forapplying the RF modulated signals to an antenna through a first filterfor wireless transmission to the leaky transmission line, (v) means forreceiving RF and spread spectrum modulated signals from the antenna viaa second filter, (vi) means for RF and spread spectrum demodulating thereceived signals using a second pseudo-random correlation code differentfrom the first correlation code, (vii) means for PCM decoding the spreadspectrum demodulated signals, (viii) means for applying the PCM decodedsignals to the telephone, whereby wireless two-way communication viasaid leaky transmission line on channels designated by the correlationcodes is provided.
 21. A system as defined in claim 20 in which thefirst and second correlation codes are variable, and means for causingvariation thereof whereby particular designated send and receive spreadspectrum channels are established.
 22. A system as defined in claim 21including a synchronization and control circuit, a second demodulatorhaving its input connected to the output of said second filter forreceiving a supervisory signal including synchronization signals, andproviding demodulated digital supervisory signals therefrom to thesynchronization and control circuit, the second demodulator using afixed predetermined correlation code for demodulation of the supervisorysignals, a second modulator having its input connected to thesynchronization and control circuit for receiving supervisory signalsand spread spectrum modulating said latter signals using a fixedpredetermined pseudo-random code different from that of the correlationcode used in the first modulator, RF modulating signals and applying thesignals via the second filter to the antenna, and means in thesynchronization and control circuit for receiving supervisory signalsfrom the telephone, generating supervisory data signals of predefinedformat and applying them to the second modulator, and for receivingsupervisory data signals of predefined format from the seconddemodulator, for translating said latter supervisory signals therefromand applying said translated signals to the telephone.
 23. A system asdefined in claim 22 including means at the synchronization and controlcircuit for deriving designated correlation codes from the receivedsupervisory signals of predefined format and for enabling the firstmodulator and demodulator to use said latter correlation codes inmodulation and demodulation respectively to establish the receive andtransmit channels for said signals.
 24. A system as defined in claim 23including means for generating and displaying data at said wirelesscommunication terminal, a data interface circuit connected to said datagenerating and displaying means, third means for spread spectrum and RFmodulating data signals received via said interface circuit and applyingthe RF modulated signals to the first filter for transmission via theantenna to the leaky transmission line, third demodulation means havingits input connected to the antenna via the second filter, and its outputconnected to the data interface circuit for applying demodulated datasignals thereto, and means connected the third modulator and demodulatorto the synchronization and control circuit for carrying signalstherefrom designative of the pseudo-random correlation codes to be usedby the third modulator and demodulator.
 25. A wireless communicationsystem comprising:(a) means at a central location for receiving aplurality of signals for communication with selected wirelesscommunication terminals, (b) means at said central location forconverting said signals to spread spectrum radio frequency signals usingcorrelation codes corresponding to particular idle channels, (c) a leakytransmission line located in a communication region within the building,(d) means for applying said spread spectrum radio frequency signals tosaid transmission line for electromagnetic radiation within said region,(e) at least one mobile wireless communication terminal adapted toreceive a predetermined one of the spread spectrum radio frequencysignals within the building and for demodulating it into an intelligiblesignal, and (f) a plurality of similar circuits each comprising aninterface means at the central location for connection to an individualjunctor of a PABX, for receiving and transmitting communication signalsfrom said junctor and for receiving and transmitting supervisory signalsfrom the PABX relating to a telephone call, a central PCM encoderconnected to the interface means for receiving signals to be transmittedto a wireless communication terminal, a modulator using a fixedpseudo-random correlation code associated with the junctor for spreadspectrum analog and generating an RF modulated signal, means forapplying the latter RF modulated signal through a transmit band limitingfilter to the leaky transmission line, means for receiving an RFmodulated signal from the leaky transmission line through a receive bandlimiting filter, a central demodulator for demodulating and despreadinga received RF modulated signal using a fixed pseudo-random correlationcode associated with said junctor for demodulating the latter signal, aPCM decoder for receiving a spread spectrum demodulated signal andapplying it to the interface means for application to said junctor, adata interface circuit connected to the former interface circuit forreceiving and transmitting data signals from and to the associatedjunctor and/or data bus of the PABX, a data channel modulator having afixed correlation code corresponding to the junctor connected to thedata interface circuit for spread spectrum and RF modulating a datasignal received therefrom and applying the RF modulated signal via thetransmit filter to the leaky transmission line, a data channeldemodulator having its input connected via the receive filter to theleaky transmission line and for applying a data signal to the datainterface circuit for transmission to the junctor or PABX data bus, acentral synchronization and control circuit connected to all saidinterface means for receiving supervisory signals from the junctorsand/or a bus of the PABX and for formulating polling and supervisorysignals of predefined format corresponding thereto and for translatingpoll messages and supervisory signals of predefined format tosupervisory signals and for applying the latter signals to the junctorsand/or bus of the PABX, a supervisory channel modulator using apredetermined supervisory channel correlation code for receiving andspread spectrum modulating said formulated polling and supervisorysignals, RF modulating the latter signal and applying the RF modulatedsignal via the transmit band limiting filter to the leaky transmissionline, a supervisory channel demodulator connected to the output of thereceive band limiting filter for RF demodulating and despreading areceived signal, and applying received poll and supervisory signals tothe synchronization and control circuit, a plurality of unidirectionalrepeaters connected serially at spaced locations in the leakytransmission line whereby an input and an output to the line aredefined, the output of the transmit band limiting filter being connectedto the input of the transmission line and the input to the receivefilter being connected to the output of the transmission line, thefrequency of the R.F. modulated signals being between approximately 150MHz and 1000 MHz.
 26. A wireless communication system comprising:(a)means at a central location for receiving a plurality of signals forcommunication with selected wireless communication terminals, (b) meansat said central location for converting said signals to spread spectrumradio frequency signals using correlation codes corresponding toparticular idle channels, (c) a leaky transmission line located in acommunication region within the building, (d) means for applying saidspread spectrum radio frequency signals to said transmission line forelectromagnetic radiation within said region, (e) at least one mobilewireless communication terminal adapted to receive a predetermined oneof the spread spectrum radio frequency signals within the building andfor demodulating it into an intelligible signal, and (f) a plurality ofsimilar circuits each comprising an interface means at the centrallocation for connection to an individual junctor of a PABX, forreceiving and transmitting communication signals from said junctor andfor receiving and transmitting supervisory signals from the PABXrelating to a telephone call, a central PCM encoder connected to theinterface means for receiving signals to be transmitted to a wirelesscommunication terminal, a modulator using a fixed pseudo-randomcorrelation code associated with the junctor for spread spectrummodulating the encoded signal and generating an RF modulated signal,means for applying the latter RF modulated signal through a transmitband limiting filter to the leaky transmission line, means for receivingan RF modulated signal from the leaky transmission line through areceive band limiting filter, a central demodulator for demodulating anddespreading a received RF modulated signal using a fixed pseudo-randomcorrelation code associated with said junctor for demodulating thelatter signal, a PCM decoder for receiving a spread spectrum demodulatedsignal and applying it to the interface means for application to saidjunctor, a data interface circuit connected to the former interfacecircuit for receiving and transmitting data signals from and to theassociated junctor and/or data bus of the PABX, a data channel spectrummodulator having a fixed correlation code corresponding to the junctorconnected to the data interface circuit for spread spectrum and RFmodulating a data signal received therefrom and applying the RFmodulated signal via the transmit filter to the leaky transmission line,a data channel demodulator having its input connected via the receivefilter to the leaky transmission line and for applying a data signal tothe data interface circuit for transmission to the junctor or PABX databus, a central synchronization and control circuit connected to all saidinterface means for receiving supervisory signals from the junctorsand/or a bus of the PABX and for formulating polling and supervisorysignals of predefined format corresponding thereto and for translatingpoll messages and supervisory signals of predefined format tosupervisory signals and for applying the latter signals to the junctorsand/or bus of the PABX, a supervisory channel modulator using apredetermined supervisory channel correlation code for receiving andspread spectrum modulating said formulated polling and supervisorysignals, RF modulating the latter signal and applying the RF modulatedsignal via the transmit band limiting filter to the leaky transmissionline, a supervisory channel demodulator connected to the output of thereceive band limiting filter for RF demodulating and despreading areceived signal, and applying received poll and supervisory signals tothe synchronization and control circuit, a plurality of unidirectionalrepeaters connected serially at spaced locations in the leakytransmission line whereby an input and an output to the line aredefined, the output of the transmit band limiting filter being connectedto the input of the transmission line and the input to the receivefilter being connected to the output of the transmission line, thetransmission line being coaxial cable having a shield containing gapssufficient to allow RF energy to radiate therefrom.